1. Field of the Invention
The present invention relates to a method for cooling oxide melts of grinding material, fire resistant material, etc. and to an apparatus for practicing such method.
2. Prior Art
Several conventional method for manufacturing molten oxides applied to zirconia-aluminous abrasives are disclosed in patents.
One of the methods is to pour the molten oxide into a carbon steel bowl (21/2" in diameter) as disclosed in Japanese Patent Publication No. 1975-16556. Another method is to solidify the molten oxide by pouring it into a void space between parallel plates having a gap (12.7-1.6 m/m) as disclosed in Japanese Patent Publication No. 1977-39193. Japanese Patent Publication No. 1982-36299 discloses a method wherein a melt of grinding material is poured into a melt of metal that has melting point below 300.degree. C. and a boiling point about 2000.degree. C. In addition, equipment along this line is provided in Japanese Patent Publication No. 1983-14816, which is an applied model of the method of Japanese Patent Publication No. 1977-39113. (All of them are provided by Norton Company).
In general, a method for producing molten oxides of grinding material or refractory material, etc. with zirconia dispersed homogenously in the resultant product requires as important conditions, appropriate control of the cooling rate, proper selection of the cooling direction, and the facillitation of detachment as well as grinding of the solidified products from the melt. In light of this, as is pointed out in Japanese Patent Application Laid-Open No. 1979-62111 (the Carborundum Company), the cooling process provided by Japanese Patent Publication No. 1975-16556 is unsatisfactory in the following points. Since the cooling direction is three-dimensional, the orientation of produced crystals is irregular. Also, since the passage to be filled is turned and bent, it is difficult for it to be filled with the molten oxide. Further, since further cooling is necessary for detachment of the solidified product of the melt, it takes more time and makes this process far less desirable in view of production efficiency. Also, the cooling rate differs greatly between the center area and the peripheral area of the solidified product. As a result, it is not feasible to obtain aluminous grinding material with zirconia dispersed evenly in it.
The method disclosed in Japanese Patent Publication No. 1977-39193 is advantageous in that since unidirectional solidification is used for cooling the molten oxide and also the cooling rate is sufficiently controlled in this method, it offers an aluminous abrasive containing homogenously dispersed zirconia. However, on the other hand, there still remain problems in this method in terms of manufacturing. Particularly, detachment of the solidified product from the melt from the parallel plates is difficult and dangerous. Furthermore, the solidified product from the melt thus obtained is flaky in form having a large area. Further, in view of the high degree of toughness that is characteristic of zirconia-alumina grinding material, the product is not suitable for coarse impact crushing carried out by the use of an impeller breaker or jaw crusher. Also, even in the apparatus provided in the above method by Japanese Patent Publication No. 1983-14186, while most of the problems are solved, the remnants of the problems are yet to be solved regarding the lack of flexibility in using the apparatus and also the need for large amount of investment capital.
On the other hand, with the method proposed by Japanese Patent Publication No. 1982-36299, an aluminous abrasive containing homogeneously dispersed zirconia can be obtained. However, separation of the abrasive grain from the metal is not easy because a metal melt bath is used for cooling. Also, in the method disclosed in Japanese Patent Publication No. 1979-62111, satisfactory results are not obtained since a large capacity is required for pouring the molten oxide in order to obtain aluminous grinding material containing homogenously dispersed zirconia by sufficiently controlling the cooling rate. Besides, detachment of the solidified product from the melt is quite difficult.